He trick Trotsky into not turning up for the funeral, severely damaging Trotsky's reputation and political prestige.

He made the most of the funeral, setting himself up as Lenin's disciple, the person who would carry on Lenin's work.

Round 2:

Krupskaya gave Lenin's secret testament to the Central Committee in May 1924, just before the Thirteenth Party Congress. If read out this would have been the end to Stalin's Career. However, Zinoviev and Kamenev urged that is should not become general knowledge because..

It was not very flattering about them because of their opposition to Lenin in 1917; this was not something they wanted to bring to the congress's attention when they hoped to become its leading lights.

they thought that Stalin presented no real threat to them or the party and they wanted Stalin's help in defeating Trotsky